I have to say that reading your posts I am quite shocked that you appear to be concerned for yourself, rather than your son. The two sources of help that are available - his father or SS - you do not want to contact. It comes across as 'me, me, me'. Forgive me if that is not the case, but I read it that way.
I do not mean to be harsh, this is obviously a terribly difficult situation and I understand that you want to protect your younger children. However, throwing your son out onto the streets, rather than ask for help or find him somewhere to go (his father for instance) seems a very cruel thing to do.
As others have said, there are organisations that can help your son - in many ways it does not matter which one, as if inappropriate they can refer your son onto the correct one. I also understand your reluctance to call SS because of your little ones. BUT it is very likely SS could become involved anyway, and the fact you have abandoned your son without seeking help will NOT look good. It is surely better for all your sakes to contact them yourself.
I wish you all well - especially your son, for whom being abandoned cannot help with his problems. We all say terrible things at times, we are human, but now is the time to make him realise you do NOT wish you had had him and get him (and you) the help and support he so desperately needs.
I wish you luck.